Is this performance typical of G11?
Posted 22 January 2013 - 06:32 AM
Posted 22 January 2013 - 06:37 AM
Posted 22 January 2013 - 07:42 AM
Have you tried calling Losmandy? (as opposed to emailing or going to their forum)
Posted 22 January 2013 - 10:40 AM
I pulled your tracking into a spreadsheet & looked at it. I found some inconsistencies, The number of intervals per hour is erratic anywhere from 12 to 17 intervals per hour and the time between those intervals is anywhere between 3" to 7". So the tracking itself isn't consistent nor is there a pattern that I can see (i.e. the dreaded 44" error), There also seems to be a connection between the brightness of the guidestar and the time between the tracking intervals. It seems that if there is a change in brightness up or down of greater than 2000 the time between the corrections is longer. This would cause the amount of correction to be greater.
Is your guidestar bright enough?
Are you having trouble "seeing" the star with the guidescope?
It seems like the guidescope may be chasing seeing. I could be wrong but it feels that way. It might be worth trying unguided vs guided to see if the problem still can be isolated that way.
Clear Dark Skies
Posted 22 January 2013 - 11:46 AM
Posted 22 January 2013 - 12:01 PM
Thanks for taking a look at the data. Maxim was set up for 3 second guide exposures when I took this data. It looks like it actually updated somewhere between 3-4 seconds depending on the cycle.
I noticed the same thing you pointed out with the brightness fluctuations. The star looked as good as I have been able to get with the OAG at this f-ratio (4.8) and the seeing was pretty good. The guide stars are definitely not pinpoints, but they are fairly bright and seem consistent. This data is typical of what I have seen on other nights with other guide stars.
I think my next course of action will be as follows:
1) Test the PE with no guiding as Hilmi suggested
2) Try unguided exposures and see if the stars look any better
3) Try guiding through a separate scope (maybe the field curvature is playing havoc with the OAG?)
4) Try the OAG with another, slower scope with a flatter field (I have a 127mm f7.5 that has a very flat field, haven't tried it yet with the new equipment).
I'll post my results.
Posted 22 January 2013 - 04:17 PM
My second setup that work pretty similar was using an Orion ST80 with SSAG in Tandem with an Orion ED80. I have so many mixed results. Some night I took long times just recording PHD settings. From 3 setup optics I have two different PHD settings written in a book so I can forget and use over and over, those that have produce very good results.
It is very possible that just trying PHD and trying different settings may help. also a miniguide isnt expensive at all to try. I got the TS9 OAG and now is just set there with no job as the miniguider is the winner.
Posted 22 January 2013 - 11:00 PM
If you physically disconnect the guide scope cable from the Losmandy mount do you still see the erratic jumps in RA? About a year ago I purchased an SBIG ST8X camera with auto guide to replace an ST402ME and external guider. I immediately had problems with erratic guiding in RA which after months of investigation was solved by the purchase of SBIGs optocoupler. According to the manual my particular Losmandy G11 should not have required one, however, it clearly fixed the problem.
Posted 22 January 2013 - 11:54 PM
Posted 23 January 2013 - 01:25 AM
if it is sticking, you can watch an inline amp meter to watch the amps jump up when it hits that point.. Motor will get hot too..
A TDM would solve your issue. i'd still worry about the motors getting too hot..
Posted 23 January 2013 - 01:33 AM
Just pulling your leg
Posted 23 January 2013 - 01:41 AM
Posted 23 January 2013 - 06:57 AM
Given that my guiding logs show a dramatic change in guide star intensity every time one of these deviations occur, I decided to take the STi out of the OAG and mount it in a 50mm guidescope to see if that would make a difference. I'm still not sure if the change in brightness is a cause or an effect of the RA guiding deviations. Well, just my luck the tube was too short to bring the STi to focus. So I replaced it in the OAG but cut an aluminum shim to keep it orthogonal in its socket (who at SBIG came up with the design of that thing? There is a huge gap in the socket and just two nylon thumbscrews to hold the camera! You can tighten it down through a wide range of lens-to-chip of angles). I digress...
With the camera better positioned in the OAG, I was actually able to get round guide stars for the first time. I let the mount guide all night long while the imaging camera took 300 second exposures. Lo and behold, the frequency and severity of RA deviations decreased (but they did not go away). The screen shot attached tells the story...fairly stable guiding graph in DEC and RA, with occasional RA deviations of up to 2.5 pixels (~14 arcsec). You can see from the background image what this is still doing to the stars.
So what does all this mean? The deviations still happen, so I'm not sure (and the log still shows a decrease in guide star brightness at those times). I don't think this is about chasing guide stars. The DEC plot never changes and it is guiding off of the same star. I think movement is occurring in RA, which causes the change in brightness by moving the star in the highly curved guider FOV. But that doesn't explain why repositioning the STi improved the tracking (some of the 300sec subs actually had no deviations, maybe 10% of them).
So I am confused. And frustrated. And tired...
Posted 23 January 2013 - 07:45 AM
Hmmmm, it looks like there IS a pattern at about 70". I'm now beginning to think grit or possibly a gall on the worm or on of the gears in the gearbox. The worm is an "easy" thing to find, the GB is, of course, a sealed unit. I'd look into swapping the GB & seeing if the problem goes away. (no $$$, just time). If it goes away the I'd contact Losmandy about a warranty replacement GB, (You'll have the proof in your tracking graphs), if not then look to the worm. If the worm is bad then again warranty replacement, if it's dirt that is also easy. I know that's not much help or consolation but there is a solution. We just haven't found it yet, it's also easy for me to say, it's not my mount, but I do understand. BTDT & hated it.
I hate those GB because you can't do any servicing on them. I guess it's time to get back to making mine.
Clear Dark Skies
Posted 23 January 2013 - 09:10 AM
I wish Maxim was easier to use
Posted 23 January 2013 - 01:11 PM
I am now back in Oman and cand do a test with PHD to validate
Posted 23 January 2013 - 01:30 PM
G11 G2 + TDM is very close to the price of a Mach1... and to those who say a TDM will outperform a Mach1, well maybe it will and maybe it won't. But mine does 0.42" peak to peak after PEM. A PE that low is in the same range as a TDM.
Maybe it will, maybe it won't huh? Mine does .11" peak to peak with the TDM... I love it when people say, maybe it will maybe it won't when I have provided logs. What happens when I provide the logs? The thread dies. People have their foot in their mouth and hands in air unable to believe the performance..
I've said it before and I'll say it again. My CGE-Pro and TDM will smoke.. SMOKE!!!! any AP, SB, highend consumer mount.
Put that in your Mach1 and smoke it..
Stock PE, 15+ range..
DSP/Aeroquest love. = 7.8
DSP/AeroQuest Love + PEC = 1.7
No PEC TDM Only = .11
Posted 23 January 2013 - 02:28 PM
But I was talking about the G11 + TDM which would be around $5400.
This post indicates 2" p-p with a G11 and TDM..
(EQ6) indicated 1.4" p-p with an EQ6. Both figures are not quite at the 0.11" p-p that you mention. I think the TDM does better if the native PE is smaller to begin with. But this is all hair-splitting, anything <1" is I would think practically comparable.
CGE Pro's particularly the newer ones seem to have better performance than G11's given that Celestron is also now guaranteeing +/- 3" raw PE. I don't think Losmandy gives such a guarantee.
That said.. I have a Baumer encoder lying around (similar to the 250 Euro Heidenhain encoder in the TDM) and one of these days I'll bolt it to my CGEM and see where that goes.
I am not saying the TDM is not a good idea, it is. I think it is way too expensive though given that the encoder - the most expensive part - is $400. I also stand by my original assertion that a G11 G2 + TDM is not a good buy compared to a Mach1 since the prices are very similar and the performance is comparable in terms of PE. And imaging performance isn't all about PE, declination guiding has been my biggest headache and that issue is non-existent with the Mach1, at least for my payloads.
Posted 23 January 2013 - 02:57 PM
It may well be as simple as some grime in the worm or somewhere in the gear box. I'd be happier suggesting that if there were a more clearly defined periodicity. It does hint at a 70s or so cycle, but I'm not really sure.
If you've already tried adjusting the mesh and have ensured that the scope is slightly East heavy, the next thing to try might be to clean and re-lubricate the worm.
Oh, one thing I found very helpful when I had a GM-8 with the older style worm and blocks was to disconnect the motor and gearbox and try turning the worm by hand. You'll be able to feel if there is any grit or roughness at any point in the cycle. Don't know if you can do that with the newer mounts, but I would assume so. This also helped me feel the difference between East and West heavy on my mount--it was quite dramatic in "smoothness".
Posted 23 January 2013 - 03:03 PM
This topic is best left for another forum. Let's get back to the OP original question..
Posted 23 January 2013 - 03:10 PM
That said I really can't wrap my head around the G11. There are many users some of whom I know personally who love the thing. Then you have this group which has inexplicable problems with it.. makes me glad I didn't go this route.
Posted 23 January 2013 - 03:19 PM
Posted 23 January 2013 - 03:28 PM
Posted 23 January 2013 - 03:47 PM
First of all lets clarify a few things
-I did run the calibration wizard first
-I ran the data gathering for a full half hour using 4 second exposures